Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nd4

Black violates an opening principle and moves again his knight. It may be tempting for White to take the now unprotected pawn with 4. Nxe5 but after 4...Qg5, White is in trouble (though 5. Bxf7+ remains playable). To maintain an advantage, White can play 4. Nxd4, 4. c3 or 4. O-O.